Novel Propulsion and Power Concepts for 21st Century Aviation

Arun K . Sehra

NASA Glenn Research Center 2 I 000 Brookpark Road

Cleveland, Oh io 44 135 USA

ABSTRACT

The air transportation for the new millennium will require revo lutionary solut ions to meeti ng public demand for improvi ng safety, reliabili ty, environmental compatibility, and affordab il ity. NASA's vis ion fo r 2 1 st

Century Aircraft is to deve lop propulsion systems that are intelligent, virtually inaud ible (outside the airport boundaries), and have near zero harmful emiss ions (C02

and NOx). This vision includes intelligent engines that will be capable of adapting to changing in ternal and external conditions to optimally accomplish the mission with mini mal human intervention. The distributed vectored propulsion wi ll replace two to four wing mounted or fuselage mounted engines by a large number of small , mini, or micro engines. And the electric drive propulsion based on fue l cell power wi ll generate electric power, which in turn will drive propu lsors to produce the des ired thrust. Such a system will completely eliminate the harmfu l emiss ions.

INTRODUCTION

To meet the pub lic demand of increased safety and capacity, reduced emissions and noise, and red uced time for trave l, NASA has established the Goal to "Revolutionize Aviation" during the next 25 years. Specific objectives are to drastical ly increase safety, reduce harmful emissions (protect local environment and g lobal climate), reduce noise, increase capacity (thruput) and increase mob ility (reduce intercontinental and in ter-city travel time).

Advanced aeropropulsion systems and computational research tools, as well as discrete technologies, will be the major contributors to 21 st Century air transportation innovation. Revolutionary propulsion systems will enable revolutionary aircraft designs that meet the need and demand ofthe fu ture.

In response to the R evolutionize Aviation Goal, NASA G lenn Research Center has deve loped an Aeropropulsion Vi s ion for 2 151 Century Aircraft E ng ines [3]. This paper reviews the NASA's Aeropropulsion Vision for 21 st Century Aviation, and noval propulsion and power concepts that are currently under development at NASA Glenn Research Center.

AEROPROPULSION VISION

NASA Glenn ' s vision is based on a phased aeropropulsion research approach to real ize the vision for 2 1 st Century air transportation (Figure I ). These phased revo lutions will be done by incorporating innovation successes from the preced ing phases to enable new revo lutions.

The Gas Turbine Revolution (as characterized by Variable Capacity, Ultra High Bypass Ratio, Inte lligent Engi nes) concentrates on component des ign and systems operability that result in propulsion systems that are compact, intelligent, and efficient fo r subsonic and supersonic transports. Adaptive controls and materials will be an integral part of the propu lsion system design. The Engine Configuration Revolution (as characterized by Distributed Vectored Propulsion systems) will focus on smart eng ine operations and distr ibuted vectored propulsion systems. Distri buted exhaust and engine concepts will be an integral part of advanced airframe des igns.

The Fuel Infrastructure Revolution will make possible the use of alternate fuels such as low carbon fuels, hydrogen and hybrids towards low emissions propulsion concepts.

The Alternate Energy Propulsion Revolution will exploit fue l cells and other high-energy power sources towards powering emiss ion less, non-gas turbine propulsion concepts.

Fig. I Propulsion System Revolutions Enabling Mobili ty

INTELLIGENT ENGINES

This is a preprint or reprint of a paper intended for presentation at a conference. Because changes may be made before formal publication, this is made available with the understanding that it will not be cited or reproduced without the permission of the author.

Novel Propulsion and Power Concepts for 21st Century Aviation

Arun K . Sehra

NASA Glenn Research Center 2 I 000 Brookpark Road

Cleveland, Oh io 44 135 USA

ABSTRACT

The air transportation for the new millennium will require revo lutionary solut ions to meeti ng public demand for improvi ng safety, reliabili ty, environmental compatibility, and affordab il ity. NASA's vis ion fo r 2 1 st

Century Aircraft is to deve lop propulsion systems that are intelligent, virtually inaud ible (outside the airport boundaries), and have near zero harmful emiss ions (C02

and NOx). This vision includes intelligent engines that will be capable of adapting to changing in ternal and external conditions to optimally accomplish the mission with mini mal human intervention. The distributed vectored propulsion wi ll replace two to four wing mounted or fuselage mounted engines by a large number of small , mini, or micro engines. And the electric drive propulsion based on fue l cell power wi ll generate electric power, which in turn will drive propu lsors to produce the des ired thrust. Such a system will completely eliminate the harmfu l emiss ions.

INTRODUCTION

To meet the pub lic demand of increased safety and capacity, reduced emissions and noise, and red uced time for trave l, NASA has established the Goal to "Revolutionize Aviation" during the next 25 years. Specific objectives are to drastical ly increase safety, reduce harmful emissions (protect local environment and g lobal climate), reduce noise, increase capacity (thruput) and increase mob ility (reduce intercontinental and in ter-city travel time).

Advanced aeropropulsion systems and computational research tools, as well as discrete technologies, will be the major contributors to 21 st Century air transportation innovation. Revolutionary propulsion systems will enable revolutionary aircraft designs that meet the need and demand ofthe fu ture.

In response to the R evolutionize Aviation Goal, NASA G lenn Research Center has deve loped an Aeropropulsion Vi s ion for 2 151 Century Aircraft E ng ines [3]. This paper reviews the NASA's Aeropropulsion Vision for 21 st Century Aviation, and noval propulsion and power concepts that are currently under development at NASA Glenn Research Center.

AEROPROPULSION VISION

NASA Glenn ' s vision is based on a phased aeropropulsion research approach to real ize the vision for 2 1 st Century air transportation (Figure I ). These phased revo lutions will be done by incorporating innovation successes from the preced ing phases to enable new revo lutions.

The Gas Turbine Revolution (as characterized by Variable Capacity, Ultra High Bypass Ratio, Inte lligent Engi nes) concentrates on component des ign and systems operability that result in propulsion systems that are compact, intelligent, and efficient fo r subsonic and supersonic transports. Adaptive controls and materials will be an integral part of the propu lsion system design. The Engine Configuration Revolution (as characterized by Distributed Vectored Propulsion systems) will focus on smart eng ine operations and distr ibuted vectored propulsion systems. Distri buted exhaust and engine concepts will be an integral part of advanced airframe des igns.

The Fuel Infrastructure Revolution will make possible the use of alternate fuels such as low carbon fuels, hydrogen and hybrids towards low emissions propulsion concepts.

The Alternate Energy Propulsion Revolution will exploit fue l cells and other high-energy power sources towards powering emiss ion less, non-gas turbine propulsion concepts.

Fig. I Propulsion System Revolutions Enabling Mobili ty

INTELLIGENT ENGINES

This is a preprint or reprint of a paper intended for presentation at a conference. Because changes may be made before formal publication, this is made available with the understanding that it will not be cited or reproduced without the permission of the author.

Novel Propulsion and Power Concepts for 21st Century Aviation

Arun K . Sehra

NASA Glenn Research Center 2 I 000 Brookpark Road

Cleveland, Oh io 44 135 USA

ABSTRACT

The air transportation for the new millennium will require revo lutionary solut ions to meeti ng public demand for improvi ng safety, reliabili ty, environmental compatibility, and affordab il ity. NASA's vis ion fo r 2 1 st

Century Aircraft is to deve lop propulsion systems that are intelligent, virtually inaud ible (outside the airport boundaries), and have near zero harmful emiss ions (C02

and NOx). This vision includes intelligent engines that will be capable of adapting to changing in ternal and external conditions to optimally accomplish the mission with mini mal human intervention. The distributed vectored propulsion wi ll replace two to four wing mounted or fuselage mounted engines by a large number of small , mini, or micro engines. And the electric drive propulsion based on fue l cell power wi ll generate electric power, which in turn will drive propu lsors to produce the des ired thrust. Such a system will completely eliminate the harmfu l emiss ions.

INTRODUCTION

To meet the pub lic demand of increased safety and capacity, reduced emissions and noise, and red uced time for trave l, NASA has established the Goal to "Revolutionize Aviation" during the next 25 years. Specific objectives are to drastical ly increase safety, reduce harmful emissions (protect local environment and g lobal climate), reduce noise, increase capacity (thruput) and increase mob ility (reduce intercontinental and in ter-city travel time).

Advanced aeropropulsion systems and computational research tools, as well as discrete technologies, will be the major contributors to 21 st Century air transportation innovation. Revolutionary propulsion systems will enable revolutionary aircraft designs that meet the need and demand ofthe fu ture.

In response to the R evolutionize Aviation Goal, NASA G lenn Research Center has deve loped an Aeropropulsion Vi s ion for 2 151 Century Aircraft E ng ines [3]. This paper reviews the NASA's Aeropropulsion Vision for 21 st Century Aviation, and noval propulsion and power concepts that are currently under development at NASA Glenn Research Center.

AEROPROPULSION VISION

NASA Glenn ' s vision is based on a phased aeropropulsion research approach to real ize the vision for 2 1 st Century air transportation (Figure I ). These phased revo lutions will be done by incorporating innovation successes from the preced ing phases to enable new revo lutions.

The Gas Turbine Revolution (as characterized by Variable Capacity, Ultra High Bypass Ratio, Inte lligent Engi nes) concentrates on component des ign and systems operability that result in propulsion systems that are compact, intelligent, and efficient fo r subsonic and supersonic transports. Adaptive controls and materials will be an integral part of the propu lsion system design. The Engine Configuration Revolution (as characterized by Distributed Vectored Propulsion systems) will focus on smart eng ine operations and distr ibuted vectored propulsion systems. Distri buted exhaust and engine concepts will be an integral part of advanced airframe des igns.

The Fuel Infrastructure Revolution will make possible the use of alternate fuels such as low carbon fuels, hydrogen and hybrids towards low emissions propulsion concepts.

The Alternate Energy Propulsion Revolution will exploit fue l cells and other high-energy power sources towards powering emiss ion less, non-gas turbine propulsion concepts.

Fig. I Propulsion System Revolutions Enabling Mobili ty

INTELLIGENT ENGINES

This is a preprint or reprint of a paper intended for presentation at a conference. Because changes may be made before formal publication, this is made available with the understanding that it will not be cited or reproduced without the permission of the author.

Advancements in the hydrocarbon-fueled gas turbine engine are rapidly approaching the limits of integration for conventional transport aircraft. Increases in bypass ratio (BPR) enabled by high temperature, high-pressure cores have ushered in a sustained era of quiet, fuel efficient subsonic propulsion. Future improvements in commercial core specific power output are limited by the growing sensitivity to NOx emission impacts and the physical size of the core-powered propulsor (or fan) for any given thrust­class of engine.

To further reduce fue l burnt and harmful emiss ions and noise, the approach make the next generation turbine engines (intelligent engines) will incorporate technologies that will autonomously adapt to the changing internal and external conditions, thereby delivering optimum / enhanced performance during the entire operating envelop. The intelligent engine techno logy focus will in the following three strategic areas:

-Intelligent Controls and Computing strategies. -Smart Components with active (or passive) control to

enhance/ optimize the performance. -Adaptive Cycles and Systems to optimize the engine performance throughout the entire operation.

Intelligent Controls and Computing

Intelligent Controls: In the area of sensors and controls, future research will also transform recent successes in physics-based multidisciplinary modeling into real-time propulsion health monitoring and management for improved safety and reduced maintenance costs. Further developments in adaptive on-board engine models, advanced component design techniques coupled with material-embedded nano-sensors and evolving information­technology capabilities (computational processing speed, data acquisition and dissemination, etc.) will allow for real­time engine condition monitoring and performance optimization.

Future vision is to make various engine systems function more autonomously from the cockpit using biologically inspired "intelligent engine" controls akin to the involuntary nervous system. This will enab le event or outcome-based decisions from the voluntary cockpit control for safer aircraft operation of increasingly complex aviation systems.

Intelligent Computing: In addition to the current effort on physics based modeling for multi-disciplinary (aero, thermo, and structural) analysis of propulsion systems, the next generation computing process wi ll have several new features. The intelligent computational environment will: provide need based information to individuals from different disciplines; compute the level of uncertainty in the computed results caused by variability in geometry, operating conditions and numerical error (probabilistic methods); select optimum number of processors for computing; and determine the use of appropriate code for desired level offidelity in the design or analysis process.

NASA Glenn Research Center is currently developing a computational environment for the design and analysis of any conceivable propulsion system (Lytle, 2000), called the Numerical Propulsion System Simulation (NPSS). NPSS

2

IGTC03-ABS-066b

(Figure 2) focuses on the integration of mUltiple disciplines such as thermodynamics, aerodynamics, structures, and heat transfer. It captures the concept of numerical zooming between O-dimensional to 1-, 2-, and 3-dimensional analysis codes.

Fig. 2 Numerical PropulSion System Simulation of a Large Commercial Turbofan Engine

The vision for NPSS is to create a "numerical test cell" enab ling full engine simu lations overnight on cost effective computing platforms. Numerical zoom ing between NPSS engine simulations and higher fide li ty representation.s of the engine components (fan, compressor, burner, turbmes, etc.) has already been demonstrated. Future augmentations will address the above mentioned intelligent computing concepts.

Smart Components for Noise and Emission Reduction

The research effort for smart components is directed at active and passive control strategies to improve performance (increased loading and operabi li ty), and reduce noise and harmful emissions. For performance improvement, NASA' s research has demonstrated rotating stall and surge instability can be significantly delayed by actively or passively contro lling (steady or fluctuating) the compressor bleed. It has also been recently demonstrated that blade loading and efficiency can be significantly enhanced by flow injection! suction on the airfoil suction surface.

For noise reduction, the key engine components that need to be addressed are Fan, Inlet, and Exhaust Nozzle. Aspirated fans with trailing edge blowing (passive) have shown significant reduction in rotor-stator interaction as well as broad band noise. Inlet and nozzle techno logies will focus on noise reduction and propulsion system operability impacts. Additional active noise suppressi~n

(such as pulsating acoustic liners) will also be employed m future inlet and nozzle systems.

While reduction is fuel bum directly translates to C02 reduction, major advances need to made in the area of combustors to reduce NOx emissions. As the latter requirement becomes more stringent, the combustor designs move towards a " lean" burning solution where the fuel/air mixture is richer in air to allow for complete combustion of the fuel. Active control of fuel/air mixture will help to reduce the NOx emission. Such combustor

Advancements in the hydrocarbon-fueled gas turbine engine are rapidly approaching the limits of integration for conventional transport aircraft. Increases in bypass ratio (BPR) enabled by high temperature, high-pressure cores have ushered in a sustained era of quiet, fuel efficient subsonic propulsion. Future improvements in commercial core specific power output are limited by the growing sensitivity to NOx emission impacts and the physical size of the core-powered propulsor (or fan) for any given thrust­class of engine.

To further reduce fue l burnt and harmful emiss ions and noise, the approach make the next generation turbine engines (intelligent engines) will incorporate technologies that will autonomously adapt to the changing internal and external conditions, thereby delivering optimum / enhanced performance during the entire operating envelop. The intelligent engine techno logy focus will in the following three strategic areas:

-Intelligent Controls and Computing strategies. -Smart Components with active (or passive) control to

enhance/ optimize the performance. -Adaptive Cycles and Systems to optimize the engine performance throughout the entire operation.

Intelligent Controls and Computing

Intelligent Controls: In the area of sensors and controls, future research will also transform recent successes in physics-based multidisciplinary modeling into real-time propulsion health monitoring and management for improved safety and reduced maintenance costs. Further developments in adaptive on-board engine models, advanced component design techniques coupled with material-embedded nano-sensors and evolving information­technology capabilities (computational processing speed, data acquisition and dissemination, etc.) will allow for real­time engine condition monitoring and performance optimization.

Future vision is to make various engine systems function more autonomously from the cockpit using biologically inspired "intelligent engine" controls akin to the involuntary nervous system. This will enab le event or outcome-based decisions from the voluntary cockpit control for safer aircraft operation of increasingly complex aviation systems.

Intelligent Computing: In addition to the current effort on physics based modeling for multi-disciplinary (aero, thermo, and structural) analysis of propulsion systems, the next generation computing process wi ll have several new features. The intelligent computational environment will: provide need based information to individuals from different disciplines; compute the level of uncertainty in the computed results caused by variability in geometry, operating conditions and numerical error (probabilistic methods); select optimum number of processors for computing; and determine the use of appropriate code for desired level offidelity in the design or analysis process.

NASA Glenn Research Center is currently developing a computational environment for the design and analysis of any conceivable propulsion system (Lytle, 2000), called the Numerical Propulsion System Simulation (NPSS). NPSS

2

IGTC03-ABS-066b

(Figure 2) focuses on the integration of mUltiple disciplines such as thermodynamics, aerodynamics, structures, and heat transfer. It captures the concept of numerical zooming between O-dimensional to 1-, 2-, and 3-dimensional analysis codes.

Fig. 2 Numerical PropulSion System Simulation of a Large Commercial Turbofan Engine

The vision for NPSS is to create a "numerical test cell" enab ling full engine simu lations overnight on cost effective computing platforms. Numerical zoom ing between NPSS engine simulations and higher fide li ty representation.s of the engine components (fan, compressor, burner, turbmes, etc.) has already been demonstrated. Future augmentations will address the above mentioned intelligent computing concepts.

Smart Components for Noise and Emission Reduction

The research effort for smart components is directed at active and passive control strategies to improve performance (increased loading and operabi li ty), and reduce noise and harmful emissions. For performance improvement, NASA' s research has demonstrated rotating stall and surge instability can be significantly delayed by actively or passively contro lling (steady or fluctuating) the compressor bleed. It has also been recently demonstrated that blade loading and efficiency can be significantly enhanced by flow injection! suction on the airfoil suction surface.

For noise reduction, the key engine components that need to be addressed are Fan, Inlet, and Exhaust Nozzle. Aspirated fans with trailing edge blowing (passive) have shown significant reduction in rotor-stator interaction as well as broad band noise. Inlet and nozzle techno logies will focus on noise reduction and propulsion system operability impacts. Additional active noise suppressi~n

(such as pulsating acoustic liners) will also be employed m future inlet and nozzle systems.

While reduction is fuel bum directly translates to C02 reduction, major advances need to made in the area of combustors to reduce NOx emissions. As the latter requirement becomes more stringent, the combustor designs move towards a " lean" burning solution where the fuel/air mixture is richer in air to allow for complete combustion of the fuel. Active control of fuel/air mixture will help to reduce the NOx emission. Such combustor

Advancements in the hydrocarbon-fueled gas turbine engine are rapidly approaching the limits of integration for conventional transport aircraft. Increases in bypass ratio (BPR) enabled by high temperature, high-pressure cores have ushered in a sustained era of quiet, fuel efficient subsonic propulsion. Future improvements in commercial core specific power output are limited by the growing sensitivity to NOx emission impacts and the physical size of the core-powered propulsor (or fan) for any given thrust­class of engine.

To further reduce fue l burnt and harmful emiss ions and noise, the approach make the next generation turbine engines (intelligent engines) will incorporate technologies that will autonomously adapt to the changing internal and external conditions, thereby delivering optimum / enhanced performance during the entire operating envelop. The intelligent engine techno logy focus will in the following three strategic areas:

-Intelligent Controls and Computing strategies. -Smart Components with active (or passive) control to

enhance/ optimize the performance. -Adaptive Cycles and Systems to optimize the engine performance throughout the entire operation.

Intelligent Controls and Computing

Intelligent Controls: In the area of sensors and controls, future research will also transform recent successes in physics-based multidisciplinary modeling into real-time propulsion health monitoring and management for improved safety and reduced maintenance costs. Further developments in adaptive on-board engine models, advanced component design techniques coupled with material-embedded nano-sensors and evolving information­technology capabilities (computational processing speed, data acquisition and dissemination, etc.) will allow for real­time engine condition monitoring and performance optimization.

Future vision is to make various engine systems function more autonomously from the cockpit using biologically inspired "intelligent engine" controls akin to the involuntary nervous system. This will enab le event or outcome-based decisions from the voluntary cockpit control for safer aircraft operation of increasingly complex aviation systems.

Intelligent Computing: In addition to the current effort on physics based modeling for multi-disciplinary (aero, thermo, and structural) analysis of propulsion systems, the next generation computing process wi ll have several new features. The intelligent computational environment will: provide need based information to individuals from different disciplines; compute the level of uncertainty in the computed results caused by variability in geometry, operating conditions and numerical error (probabilistic methods); select optimum number of processors for computing; and determine the use of appropriate code for desired level offidelity in the design or analysis process.

NASA Glenn Research Center is currently developing a computational environment for the design and analysis of any conceivable propulsion system (Lytle, 2000), called the Numerical Propulsion System Simulation (NPSS). NPSS

2

IGTC03-ABS-066b

(Figure 2) focuses on the integration of mUltiple disciplines such as thermodynamics, aerodynamics, structures, and heat transfer. It captures the concept of numerical zooming between O-dimensional to 1-, 2-, and 3-dimensional analysis codes.

Fig. 2 Numerical PropulSion System Simulation of a Large Commercial Turbofan Engine

The vision for NPSS is to create a "numerical test cell" enab ling full engine simu lations overnight on cost effective computing platforms. Numerical zoom ing between NPSS engine simulations and higher fide li ty representation.s of the engine components (fan, compressor, burner, turbmes, etc.) has already been demonstrated. Future augmentations will address the above mentioned intelligent computing concepts.

Smart Components for Noise and Emission Reduction

The research effort for smart components is directed at active and passive control strategies to improve performance (increased loading and operabi li ty), and reduce noise and harmful emissions. For performance improvement, NASA' s research has demonstrated rotating stall and surge instability can be significantly delayed by actively or passively contro lling (steady or fluctuating) the compressor bleed. It has also been recently demonstrated that blade loading and efficiency can be significantly enhanced by flow injection! suction on the airfoil suction surface.

For noise reduction, the key engine components that need to be addressed are Fan, Inlet, and Exhaust Nozzle. Aspirated fans with trailing edge blowing (passive) have shown significant reduction in rotor-stator interaction as well as broad band noise. Inlet and nozzle techno logies will focus on noise reduction and propulsion system operability impacts. Additional active noise suppressi~n

(such as pulsating acoustic liners) will also be employed m future inlet and nozzle systems.

While reduction is fuel bum directly translates to C02 reduction, major advances need to made in the area of combustors to reduce NOx emissions. As the latter requirement becomes more stringent, the combustor designs move towards a " lean" burning solution where the fuel/air mixture is richer in air to allow for complete combustion of the fuel. Active control of fuel/air mixture will help to reduce the NOx emission. Such combustor

,-

designs are prone to instability due to thermo-acoustic driven pressure osci llations. Active contro l of such oscillations wi ll allow for more efficient combustor designs.

Adaptive Cvcles and Systems

Adaptive technologies for turbine engines will center on performance and operab ili ty, utilizing research in fluidics, structures and materiaJ system capabi lities, and advanced variable cycle engine configurations. FundamentaJ fluidic technology wi ll enab le "virtuaJ" aerodynamic shapes, providing inlet and nozzle area control and peak compressor and turbine efficiency operation over a wide range offlight speeds.

Flow Control and Management: Active and passive redistribution of boundary layer flows within the engi ne will have a profound adaptab ili ty effect on the overall propulsion performance and weight by minimizing mechanicaJ actuation and associated life and leakage losses. For example, turbine flow area control through fluidics and active seals will enable re-optimization of the engine BPR between takeoff and cruise. This wi ll reconcile design constraints for reduced takeoff emissions and improved cruise fuel-efficiency across the transport a ircraft flight envelope. Acoustical fluidic contro l of inlet and nozzle boundary layers could be teamed with active ly pulsed noise attenuating liners, thereby maxllTIlzll1g the dual applicability of a single integrated technology.

Morphing Structures: MechanicaJ and structuraJ variab ility will aJso undergo a revolution with the advent of active/passive shape-memory materials and tailored aeroelastic design capab ili ty or "morphing". Similar in effect to the fluidic virtual shape technologies, future shape-memory materials will be emp loyed in a variety of component areas. Inlet lip radius/ sharpness, coup led with anti -icing technology, cou ld be made to change shape between takeoff and cruise, enab ling high takeoff airflow without compromising the high cruise efficiency and low drag afforded by a sharper inlet lip. Shape memory inlet and nozzle contraction area variab ili ty wi ll improve engine performance and operabi li ty without the weight from mechanicaJ actuation. App lication of shape-memory materials to turbomachinery will yie ld camber reshaping (for loading and efficiency optimization and operab ili ty). The large internal changes in engine temperature environments and speeds readily provide un tapped thermal and centrifugaJ forces from which to team pass ive, structural shape contro l. Variable-speed gearboxes are another ferti le application of shape-memory materia ls, providing optimum matching of engine high and low pressure spool speeds throughout the flight enve lope, and maximizing the utility of the gearbox.

Adaptive Materials: Future material systems will not only be designed for thei r properties but also for their unique functionality. Crystalline grown metallics optimized for their application-specific grai n boundary properties may contain lattice-encoded DNA-li ke properties. These wi ll be capable of changing grain boundary size through active and/or passive st imuli thereby

3

JGTC03-ABS-066b

preventing component failures. Similar chemicaJly encoded properties for coatings and compliant layers will passively provide se lf-healing protection against surface delamination, oxidation, and spalling.

Future matrix fibers (used in MMC, CMC, and PMC materials) wi ll not on ly provide structuraJ reinforcement but aJso serve as an embedded conduit for information exchange to and fro m the intelligent engine control, as described under Fundamentals.

Nanotu

Fig. 3 Nanotechno logy MateriaJs

High conductivi ty fibers such as carbon nano-tubes (F igure 3) will simulate nerve ganglia to passively co llect component diagnostic data. These same fibers may aJso be used to supply messages and adjust the configuration to optimize operating characteristics or to prevent/control component fai lures.

Adaptive Cycles: Thermodynamic cycle modifications and accompanying structuraJ flowpath changes w ill also produce propulsion system adaptability. Bladerow by bladerow counter-rotating, concentric spool engines employing blade-on-blade technologies and advanced materia ls wi ll stretch the limits of the var iab le cyc le engine. These propulsion systems will enable the use of extremely low-weight (strength-compromised) composites by turning the turbomachinery , inside out". This wi ll put the blades in compressive rather than tensi le stress. Bladerow counter-rotation will further reduce the required rotational spoo l speed per turbomachinery loading, enabling acoustically superior tip-shrouded counter-rotatlng fans. Other modified Brayton cycle adaptations will include off­axis cores powering ultra-high pressure combustion and serving as topping cyc les for peak-power takeoff thrust without compromising the optimum cycle operation for cruise. Inter-turbine and even inter-stage turbine combustion configurations are being investigated for their large impacts on cycle adaptability over diverse missions. These modified Brayton cycles aJso intrinsically offer leaner combustion and reduced emissions, but challenge state-of-the-art stabi li ty practices.

DISTRlliUTED VECTORED PROPULSION

,-

designs are prone to instability due to thermo-acoustic driven pressure osci llations. Active contro l of such oscillations wi ll allow for more efficient combustor designs.

Adaptive Cvcles and Systems

Adaptive technologies for turbine engines will center on performance and operab ili ty, utilizing research in fluidics, structures and materiaJ system capabi lities, and advanced variable cycle engine configurations. FundamentaJ fluidic technology wi ll enab le "virtuaJ" aerodynamic shapes, providing inlet and nozzle area control and peak compressor and turbine efficiency operation over a wide range offlight speeds.

Flow Control and Management: Active and passive redistribution of boundary layer flows within the engi ne will have a profound adaptab ili ty effect on the overall propulsion performance and weight by minimizing mechanicaJ actuation and associated life and leakage losses. For example, turbine flow area control through fluidics and active seals will enable re-optimization of the engine BPR between takeoff and cruise. This wi ll reconcile design constraints for reduced takeoff emissions and improved cruise fuel-efficiency across the transport a ircraft flight envelope. Acoustical fluidic contro l of inlet and nozzle boundary layers could be teamed with active ly pulsed noise attenuating liners, thereby maxllTIlzll1g the dual applicability of a single integrated technology.

Morphing Structures: MechanicaJ and structuraJ variab ility will aJso undergo a revolution with the advent of active/passive shape-memory materials and tailored aeroelastic design capab ili ty or "morphing". Similar in effect to the fluidic virtual shape technologies, future shape-memory materials will be emp loyed in a variety of component areas. Inlet lip radius/ sharpness, coup led with anti -icing technology, cou ld be made to change shape between takeoff and cruise, enab ling high takeoff airflow without compromising the high cruise efficiency and low drag afforded by a sharper inlet lip. Shape memory inlet and nozzle contraction area variab ili ty wi ll improve engine performance and operabi li ty without the weight from mechanicaJ actuation. App lication of shape-memory materials to turbomachinery will yie ld camber reshaping (for loading and efficiency optimization and operab ili ty). The large internal changes in engine temperature environments and speeds readily provide un tapped thermal and centrifugaJ forces from which to team pass ive, structural shape contro l. Variable-speed gearboxes are another ferti le application of shape-memory materia ls, providing optimum matching of engine high and low pressure spool speeds throughout the flight enve lope, and maximizing the utility of the gearbox.

Adaptive Materials: Future material systems will not only be designed for thei r properties but also for their unique functionality. Crystalline grown metallics optimized for their application-specific grai n boundary properties may contain lattice-encoded DNA-li ke properties. These wi ll be capable of changing grain boundary size through active and/or passive st imuli thereby

3

JGTC03-ABS-066b

preventing component failures. Similar chemicaJly encoded properties for coatings and compliant layers will passively provide se lf-healing protection against surface delamination, oxidation, and spalling.

Future matrix fibers (used in MMC, CMC, and PMC materials) wi ll not on ly provide structuraJ reinforcement but aJso serve as an embedded conduit for information exchange to and fro m the intelligent engine control, as described under Fundamentals.

Nanotu

Fig. 3 Nanotechno logy MateriaJs

High conductivi ty fibers such as carbon nano-tubes (F igure 3) will simulate nerve ganglia to passively co llect component diagnostic data. These same fibers may aJso be used to supply messages and adjust the configuration to optimize operating characteristics or to prevent/control component fai lures.

Adaptive Cycles: Thermodynamic cycle modifications and accompanying structuraJ flowpath changes w ill also produce propulsion system adaptability. Bladerow by bladerow counter-rotating, concentric spool engines employing blade-on-blade technologies and advanced materia ls wi ll stretch the limits of the var iab le cyc le engine. These propulsion systems will enable the use of extremely low-weight (strength-compromised) composites by turning the turbomachinery , inside out". This wi ll put the blades in compressive rather than tensi le stress. Bladerow counter-rotation will further reduce the required rotational spoo l speed per turbomachinery loading, enabling acoustically superior tip-shrouded counter-rotatlng fans. Other modified Brayton cycle adaptations will include off­axis cores powering ultra-high pressure combustion and serving as topping cyc les for peak-power takeoff thrust without compromising the optimum cycle operation for cruise. Inter-turbine and even inter-stage turbine combustion configurations are being investigated for their large impacts on cycle adaptability over diverse missions. These modified Brayton cycles aJso intrinsically offer leaner combustion and reduced emissions, but challenge state-of-the-art stabi li ty practices.

DISTRlliUTED VECTORED PROPULSION

,-

designs are prone to instability due to thermo-acoustic driven pressure osci llations. Active contro l of such oscillations wi ll allow for more efficient combustor designs.

Adaptive Cvcles and Systems

Adaptive technologies for turbine engines will center on performance and operab ili ty, utilizing research in fluidics, structures and materiaJ system capabi lities, and advanced variable cycle engine configurations. FundamentaJ fluidic technology wi ll enab le "virtuaJ" aerodynamic shapes, providing inlet and nozzle area control and peak compressor and turbine efficiency operation over a wide range offlight speeds.

Flow Control and Management: Active and passive redistribution of boundary layer flows within the engi ne will have a profound adaptab ili ty effect on the overall propulsion performance and weight by minimizing mechanicaJ actuation and associated life and leakage losses. For example, turbine flow area control through fluidics and active seals will enable re-optimization of the engine BPR between takeoff and cruise. This wi ll reconcile design constraints for reduced takeoff emissions and improved cruise fuel-efficiency across the transport a ircraft flight envelope. Acoustical fluidic contro l of inlet and nozzle boundary layers could be teamed with active ly pulsed noise attenuating liners, thereby maxllTIlzll1g the dual applicability of a single integrated technology.

Morphing Structures: MechanicaJ and structuraJ variab ility will aJso undergo a revolution with the advent of active/passive shape-memory materials and tailored aeroelastic design capab ili ty or "morphing". Similar in effect to the fluidic virtual shape technologies, future shape-memory materials will be emp loyed in a variety of component areas. Inlet lip radius/ sharpness, coup led with anti -icing technology, cou ld be made to change shape between takeoff and cruise, enab ling high takeoff airflow without compromising the high cruise efficiency and low drag afforded by a sharper inlet lip. Shape memory inlet and nozzle contraction area variab ili ty wi ll improve engine performance and operabi li ty without the weight from mechanicaJ actuation. App lication of shape-memory materials to turbomachinery will yie ld camber reshaping (for loading and efficiency optimization and operab ili ty). The large internal changes in engine temperature environments and speeds readily provide un tapped thermal and centrifugaJ forces from which to team pass ive, structural shape contro l. Variable-speed gearboxes are another ferti le application of shape-memory materia ls, providing optimum matching of engine high and low pressure spool speeds throughout the flight enve lope, and maximizing the utility of the gearbox.

Adaptive Materials: Future material systems will not only be designed for thei r properties but also for their unique functionality. Crystalline grown metallics optimized for their application-specific grai n boundary properties may contain lattice-encoded DNA-li ke properties. These wi ll be capable of changing grain boundary size through active and/or passive st imuli thereby

3

JGTC03-ABS-066b

preventing component failures. Similar chemicaJly encoded properties for coatings and compliant layers will passively provide se lf-healing protection against surface delamination, oxidation, and spalling.

Future matrix fibers (used in MMC, CMC, and PMC materials) wi ll not on ly provide structuraJ reinforcement but aJso serve as an embedded conduit for information exchange to and fro m the intelligent engine control, as described under Fundamentals.

Nanotu

Fig. 3 Nanotechno logy MateriaJs

High conductivi ty fibers such as carbon nano-tubes (F igure 3) will simulate nerve ganglia to passively co llect component diagnostic data. These same fibers may aJso be used to supply messages and adjust the configuration to optimize operating characteristics or to prevent/control component fai lures.

Adaptive Cycles: Thermodynamic cycle modifications and accompanying structuraJ flowpath changes w ill also produce propulsion system adaptability. Bladerow by bladerow counter-rotating, concentric spool engines employing blade-on-blade technologies and advanced materia ls wi ll stretch the limits of the var iab le cyc le engine. These propulsion systems will enable the use of extremely low-weight (strength-compromised) composites by turning the turbomachinery , inside out". This wi ll put the blades in compressive rather than tensi le stress. Bladerow counter-rotation will further reduce the required rotational spoo l speed per turbomachinery loading, enabling acoustically superior tip-shrouded counter-rotatlng fans. Other modified Brayton cycle adaptations will include off­axis cores powering ultra-high pressure combustion and serving as topping cyc les for peak-power takeoff thrust without compromising the optimum cycle operation for cruise. Inter-turbine and even inter-stage turbine combustion configurations are being investigated for their large impacts on cycle adaptability over diverse missions. These modified Brayton cycles aJso intrinsically offer leaner combustion and reduced emissions, but challenge state-of-the-art stabi li ty practices.

DISTRlliUTED VECTORED PROPULSION

With the advent of the high bypass ratio turbofan, research has promoted higher temperature more thermally efficient smaller cores to power larger and larger fans for propu ls ion. These smaller ul tra-effic ient cores will someday reach practical economic limits in manufacturing size. Simi larly the larger fans will also reach limits in their manufacturability and ai rcraft integratab ili ty. At present the current state-of-the-art design BPR continues to grow, resulting in larger fans (eventually requ iring geari ng), increased ai rcraft integration challenges (necessitating high wing aircraft designs, etc.), and growing fan acoustic challenges. To circumvent these eventual limits, technologies affording highly integrated propu ls ion and airframe configurations must be pursued. Airframe­integrated propulsion and power configurations centered on distributed propulsion and capitalizi ng on techno logies realized through the Gas Turbine Revolution wil l usher in the future ai r transportation system. The distributed propulSion concept is based on rep lacing the conventionally smal l number of discrete engines with a large number of smal l or mini propulsion systems as defined in the following table.

Tab le I Maximum Thrust of Various Engine Class

Engine Micro Mini Small Mediu Large class m Max < 10 10 to 100 to 1000 to 10000< Thrust < 100 < 1000 <10000 (lb)

Distributed propulsion broadly describes a var iety of configurations that can be classified into three main categories: Distributed Engi nes (including small, mini, and micro engine systems), Common-Core Multi­Fans/Propulsors, and Distri buted Exhaust. In all three categories, the forward thrust delivered by the propuls ion system remains as the conventional large engine counterpart (mass flow times exhaust veloci ty). Strategic distr ibution of the exhausting mass flow affords direct and indirect propulsion and airframe system performance benefits that can ultimately enab le new ai rcraft missions beyond what is achievable with the state-of-the-art turbofan concepts.

Distr ibuted E ngines

The category of Distributed Engines encompasses decentralized propuls ion systems and utilizes separate smal ler powerplants strategically deployed over (or embedded) the aircraft. Examples ofthis type of distributed propulsion might include small or mini engines (Figure 4) deployed across the wingspan and fuselage, and micro­turbine engines (Figures 5) embedded in the ai rcraft surface for flow/circulation-control and thrust. Severe performance penalties manifest in mini-engine systems are principally due to boundary layer effects of the fluid being on the same geometric scale as the propulsion system. The challenge of manufacturing tolerances that can be economically observed in these engines a lso severely impacts their performance and cost. Therefore mini and micro engine

4

IGTC03-ABS-066b

propulsion must " buy its way on" the aircraft. It must afford greater benefits in other areas, such as noise and drag reduction, or by enabling a superior integrated aircraft/engine system.

Fig. 4 Distributed Engines embedded in the wing and body

Laterally distributed engines will afford simi lar aerodynamic and acoustic benefits as those described for the high aspect-ratio wi ng trail ing edge nozzle. Additional aircraft integration of supporting fluidic technologies using distr ibution engines could provide more dramat ic transport mission impacts.

Fig. 5 Rad ial inflow turbine of a micro engine

As much as 3-5% total aircraft fuel burn reduction might be realized from boundary layer ingestion employing small to min i engine distributed propu lsion. This performance benefit may be enhanced in a hybrid system utilizing micro engines to energize the low-momentum boundary layer flow. This benefit can only be realized if the micro engine fue l consumption is low (again scaveng ing of waste heat would be advantageous as described by the Distributed Exhaust concept). Because of their small s ize, extremely high specific-strength composite materia ls may be used in small and mi ni engines with less statistical failure due to defects. The reduced s ize al lows practical, cost-effective manufacturing of these advanced­material structures. Success of the small and mini engine propu ls ion deployed laterally across the wing is dependent on exploiting technologies that are best realized in the reduced sized.

Micro engines themselves can provide distributed propulsion and exhibit large thrust to weight potential . Because of their size, low Reynolds number fluid effects,

With the advent of the high bypass ratio turbofan, research has promoted higher temperature more thermally efficient smaller cores to power larger and larger fans for propu ls ion. These smaller ul tra-effic ient cores will someday reach practical economic limits in manufacturing size. Simi larly the larger fans will also reach limits in their manufacturability and ai rcraft integratab ili ty. At present the current state-of-the-art design BPR continues to grow, resulting in larger fans (eventually requ iring geari ng), increased ai rcraft integration challenges (necessitating high wing aircraft designs, etc.), and growing fan acoustic challenges. To circumvent these eventual limits, technologies affording highly integrated propu ls ion and airframe configurations must be pursued. Airframe­integrated propulsion and power configurations centered on distributed propulsion and capitalizi ng on techno logies realized through the Gas Turbine Revolution wil l usher in the future ai r transportation system. The distributed propulSion concept is based on rep lacing the conventionally smal l number of discrete engines with a large number of smal l or mini propulsion systems as defined in the following table.

Tab le I Maximum Thrust of Various Engine Class

Engine Micro Mini Small Mediu Large class m Max < 10 10 to 100 to 1000 to 10000< Thrust < 100 < 1000 <10000 (lb)

Distributed propulsion broadly describes a var iety of configurations that can be classified into three main categories: Distributed Engi nes (including small, mini, and micro engine systems), Common-Core Multi­Fans/Propulsors, and Distri buted Exhaust. In all three categories, the forward thrust delivered by the propuls ion system remains as the conventional large engine counterpart (mass flow times exhaust veloci ty). Strategic distr ibution of the exhausting mass flow affords direct and indirect propulsion and airframe system performance benefits that can ultimately enab le new ai rcraft missions beyond what is achievable with the state-of-the-art turbofan concepts.

Distr ibuted E ngines

The category of Distributed Engines encompasses decentralized propuls ion systems and utilizes separate smal ler powerplants strategically deployed over (or embedded) the aircraft. Examples ofthis type of distributed propulsion might include small or mini engines (Figure 4) deployed across the wingspan and fuselage, and micro­turbine engines (Figures 5) embedded in the ai rcraft surface for flow/circulation-control and thrust. Severe performance penalties manifest in mini-engine systems are principally due to boundary layer effects of the fluid being on the same geometric scale as the propulsion system. The challenge of manufacturing tolerances that can be economically observed in these engines a lso severely impacts their performance and cost. Therefore mini and micro engine

4

IGTC03-ABS-066b

propulsion must " buy its way on" the aircraft. It must afford greater benefits in other areas, such as noise and drag reduction, or by enabling a superior integrated aircraft/engine system.

Fig. 4 Distributed Engines embedded in the wing and body

Laterally distributed engines will afford simi lar aerodynamic and acoustic benefits as those described for the high aspect-ratio wi ng trail ing edge nozzle. Additional aircraft integration of supporting fluidic technologies using distr ibution engines could provide more dramat ic transport mission impacts.

Fig. 5 Rad ial inflow turbine of a micro engine

As much as 3-5% total aircraft fuel burn reduction might be realized from boundary layer ingestion employing small to min i engine distributed propu lsion. This performance benefit may be enhanced in a hybrid system utilizing micro engines to energize the low-momentum boundary layer flow. This benefit can only be realized if the micro engine fue l consumption is low (again scaveng ing of waste heat would be advantageous as described by the Distributed Exhaust concept). Because of their small s ize, extremely high specific-strength composite materia ls may be used in small and mi ni engines with less statistical failure due to defects. The reduced s ize al lows practical, cost-effective manufacturing of these advanced­material structures. Success of the small and mini engine propu ls ion deployed laterally across the wing is dependent on exploiting technologies that are best realized in the reduced sized.

Micro engines themselves can provide distributed propulsion and exhibit large thrust to weight potential . Because of their size, low Reynolds number fluid effects,

With the advent of the high bypass ratio turbofan, research has promoted higher temperature more thermally efficient smaller cores to power larger and larger fans for propu ls ion. These smaller ul tra-effic ient cores will someday reach practical economic limits in manufacturing size. Simi larly the larger fans will also reach limits in their manufacturability and ai rcraft integratab ili ty. At present the current state-of-the-art design BPR continues to grow, resulting in larger fans (eventually requ iring geari ng), increased ai rcraft integration challenges (necessitating high wing aircraft designs, etc.), and growing fan acoustic challenges. To circumvent these eventual limits, technologies affording highly integrated propu ls ion and airframe configurations must be pursued. Airframe­integrated propulsion and power configurations centered on distributed propulsion and capitalizi ng on techno logies realized through the Gas Turbine Revolution wil l usher in the future ai r transportation system. The distributed propulSion concept is based on rep lacing the conventionally smal l number of discrete engines with a large number of smal l or mini propulsion systems as defined in the following table.

Tab le I Maximum Thrust of Various Engine Class

Engine Micro Mini Small Mediu Large class m Max < 10 10 to 100 to 1000 to 10000< Thrust < 100 < 1000 <10000 (lb)

Distributed propulsion broadly describes a var iety of configurations that can be classified into three main categories: Distributed Engi nes (including small, mini, and micro engine systems), Common-Core Multi­Fans/Propulsors, and Distri buted Exhaust. In all three categories, the forward thrust delivered by the propuls ion system remains as the conventional large engine counterpart (mass flow times exhaust veloci ty). Strategic distr ibution of the exhausting mass flow affords direct and indirect propulsion and airframe system performance benefits that can ultimately enab le new ai rcraft missions beyond what is achievable with the state-of-the-art turbofan concepts.

Distr ibuted E ngines

The category of Distributed Engines encompasses decentralized propuls ion systems and utilizes separate smal ler powerplants strategically deployed over (or embedded) the aircraft. Examples ofthis type of distributed propulsion might include small or mini engines (Figure 4) deployed across the wingspan and fuselage, and micro­turbine engines (Figures 5) embedded in the ai rcraft surface for flow/circulation-control and thrust. Severe performance penalties manifest in mini-engine systems are principally due to boundary layer effects of the fluid being on the same geometric scale as the propulsion system. The challenge of manufacturing tolerances that can be economically observed in these engines a lso severely impacts their performance and cost. Therefore mini and micro engine

4

IGTC03-ABS-066b

propulsion must " buy its way on" the aircraft. It must afford greater benefits in other areas, such as noise and drag reduction, or by enabling a superior integrated aircraft/engine system.

Fig. 4 Distributed Engines embedded in the wing and body

Laterally distributed engines will afford simi lar aerodynamic and acoustic benefits as those described for the high aspect-ratio wi ng trail ing edge nozzle. Additional aircraft integration of supporting fluidic technologies using distr ibution engines could provide more dramat ic transport mission impacts.

Fig. 5 Rad ial inflow turbine of a micro engine

As much as 3-5% total aircraft fuel burn reduction might be realized from boundary layer ingestion employing small to min i engine distributed propu lsion. This performance benefit may be enhanced in a hybrid system utilizing micro engines to energize the low-momentum boundary layer flow. This benefit can only be realized if the micro engine fue l consumption is low (again scaveng ing of waste heat would be advantageous as described by the Distributed Exhaust concept). Because of their small s ize, extremely high specific-strength composite materia ls may be used in small and mi ni engines with less statistical failure due to defects. The reduced s ize al lows practical, cost-effective manufacturing of these advanced­material structures. Success of the small and mini engine propu ls ion deployed laterally across the wing is dependent on exploiting technologies that are best realized in the reduced sized.

Micro engines themselves can provide distributed propulsion and exhibit large thrust to weight potential . Because of their size, low Reynolds number fluid effects,

engine manufacturing tolerances and corresponding impacts on seals and clearances, 3-D turbomachinery shapes, and combustion efficiency are primary technical challenges for these propulsion systems. Currently, parts at the micro-scale can only be produced in two dimensions, resembling extruded parts. This efficiency limitation on the rotating components will be overcome with material and manufacturing technologies. These will enable three­dimensional shaping of airfoils and allowing new micro­scale engine configurations with reduced stress concentrations inherent in the current two-dimensional prototypes. Other factors affecting the structural/mechanical design of these micro-engines are the typically high rotational speeds, which may exceed 2 million RPMs. These high speeds are achievable due to reduced-scale inertial loads, but will demand non­lubricated air-bearings to surpass the common modes of failure observed in research prototypes.

Though the physical engine scale is decreased, the chemical reaction times remain constant and will require technology innovation to regain lost combustion efficiency. A very general rule for mini- and micro-engines is that both specific fuel consumption (SFC) and thrust-to-weight ratio increase as thrust and size decrease. To become a viable primary propulsion source, SFC reductions to near current macro-engine levels must accompany the increased thrust­to-weight ratios already achievab le in mini and micro engines.

Distributed engine concepts will enab le a var iety of attractive airframe configurations affording both performance and operational benefits. Large engine production rates, lower development cost and cycle time, and line-replaceable-unit elimination of on-the-wing engine maintenance could reduce the life cycle cost by as much as 50%. Aircraft safety will be enhanced through engine redundancy and semi-redundant propulsion control of the aircraft. Dual use of the ai rframe structure will dramatically reduce the overall system weight, and afford holistic system noise reduction opportunities beyond those attainable with discrete engines. Principle technologies that will afford the greatest potential for realizing micro engine propu lsion success include: innovative combustion techniques, processing of SiC and other advanced micro engine material for improved 3D designs, and integral autonomous controls coupled with sub-micro sensors assuring engine array reliability.

Common-Core Multi- FanslPropulsors

The category of Common-Core Multi-FanslPropulsors entails the packaging of multiple thrust fans powered by a central engi ne core (Figure 6). The advantage of these configurations is that they provide ultra high BPR engine with higher propulsive efficiency without necessitating radical ai rframe changes (such as high wing designs) to accommodate a single large turbofan engine. The principle challenges of this approach are power transmission weight and losses. These challenges may be somewhat mitigated by the variable gearbox technologies previously developed under the Gas Turbine Revolution, or by emp loying blade-on-blade manifolded tip-turbines on the fans. These challenges could also be circumvented

5

IGTC03-ABS-066b

using direct-drive tandem fans (i.e. axially aligned fans with separate inlets for and aft of the common core) rather than the s ide-by-side configuration. Another potential configuration uses the core exhaust to drive two off-axis turbines that are attached to direct-drive fans. Multi-fan cores will require innovative separate inlets to realize their full BPR and aircraft integration benefit. This will require lightweight structures and possibly flow control to minimize weight and inlet performance losses.

The commonly shared performance challenges assoc iated with all forms of distributed propulsion (Iow­Reynolds number flows, boundary-l ayer interactions, and fuel management systems) will be surpassed during this research phase using those technologies and discipline capabilities (aerodynamic, mechanical, materials, structures, manufacturing, etc.) outlined for the Gas Turbine Revolution . The highly integrated Distributed Vectored Propulsion systems for future subsonic and superson ic transports will incorporate V/STOL and Propulsion Controlled Aircraft (PCA) capabilities, and capitalize on intelligent, self-healing properties.

Fig. 6 Common-Core, Multi-Propulsor Engines

Distributed Exhaust

The category of Distributed Exhaust entails using a central engine powerplant with a ducted nozzle(s) for strategic deployment of thrust on the aircraft. Distributed exhaust configurations suffer nozzle viscous losses in performance and will likely only "buy their way on" to aircraft systems exhibiting extreme sensitivity to low-speed li ft and/or cru ise drag. Therefore, distributed exhaust systems will be better suited to supersonic cruise applications, where noise-sizing for takeoff fie ld length and sustained supersonic cruise drag are the most dominant and least reconcilable constraints (Figure 7).

High aspect ratio nozzles for commercial supersonic cru ise vehicles promise both noise and nozzle weight reduction potential. The projected sideline noise reduction using a wing trailing edge 2-D mixer/ejector nozzle with comparatively small exhaust height may be as much as I OdB (due to increased ambient jet mixing, improved ejector internal penetration and mixing, and increased liner attenuabi li ty resulting from naturally higher frequencies and surface areas). In addition, the high aspect ratio geometrically produces a shorter nozzle for an equal nozzle

engine manufacturing tolerances and corresponding impacts on seals and clearances, 3-D turbomachinery shapes, and combustion efficiency are primary technical challenges for these propulsion systems. Currently, parts at the micro-scale can only be produced in two dimensions, resembling extruded parts. This efficiency limitation on the rotating components will be overcome with material and manufacturing technologies. These will enable three­dimensional shaping of airfoils and allowing new micro­scale engine configurations with reduced stress concentrations inherent in the current two-dimensional prototypes. Other factors affecting the structural/mechanical design of these micro-engines are the typically high rotational speeds, which may exceed 2 million RPMs. These high speeds are achievable due to reduced-scale inertial loads, but will demand non­lubricated air-bearings to surpass the common modes of failure observed in research prototypes.

Though the physical engine scale is decreased, the chemical reaction times remain constant and will require technology innovation to regain lost combustion efficiency. A very general rule for mini- and micro-engines is that both specific fuel consumption (SFC) and thrust-to-weight ratio increase as thrust and size decrease. To become a viable primary propulsion source, SFC reductions to near current macro-engine levels must accompany the increased thrust­to-weight ratios already achievab le in mini and micro engines.

Distributed engine concepts will enab le a var iety of attractive airframe configurations affording both performance and operational benefits. Large engine production rates, lower development cost and cycle time, and line-replaceable-unit elimination of on-the-wing engine maintenance could reduce the life cycle cost by as much as 50%. Aircraft safety will be enhanced through engine redundancy and semi-redundant propulsion control of the aircraft. Dual use of the ai rframe structure will dramatically reduce the overall system weight, and afford holistic system noise reduction opportunities beyond those attainable with discrete engines. Principle technologies that will afford the greatest potential for realizing micro engine propu lsion success include: innovative combustion techniques, processing of SiC and other advanced micro engine material for improved 3D designs, and integral autonomous controls coupled with sub-micro sensors assuring engine array reliability.

Common-Core Multi- FanslPropulsors

The category of Common-Core Multi-FanslPropulsors entails the packaging of multiple thrust fans powered by a central engi ne core (Figure 6). The advantage of these configurations is that they provide ultra high BPR engine with higher propulsive efficiency without necessitating radical ai rframe changes (such as high wing designs) to accommodate a single large turbofan engine. The principle challenges of this approach are power transmission weight and losses. These challenges may be somewhat mitigated by the variable gearbox technologies previously developed under the Gas Turbine Revolution, or by emp loying blade-on-blade manifolded tip-turbines on the fans. These challenges could also be circumvented

5

IGTC03-ABS-066b

using direct-drive tandem fans (i.e. axially aligned fans with separate inlets for and aft of the common core) rather than the s ide-by-side configuration. Another potential configuration uses the core exhaust to drive two off-axis turbines that are attached to direct-drive fans. Multi-fan cores will require innovative separate inlets to realize their full BPR and aircraft integration benefit. This will require lightweight structures and possibly flow control to minimize weight and inlet performance losses.

The commonly shared performance challenges assoc iated with all forms of distributed propulsion (Iow­Reynolds number flows, boundary-l ayer interactions, and fuel management systems) will be surpassed during this research phase using those technologies and discipline capabilities (aerodynamic, mechanical, materials, structures, manufacturing, etc.) outlined for the Gas Turbine Revolution . The highly integrated Distributed Vectored Propulsion systems for future subsonic and superson ic transports will incorporate V/STOL and Propulsion Controlled Aircraft (PCA) capabilities, and capitalize on intelligent, self-healing properties.

Fig. 6 Common-Core, Multi-Propulsor Engines

Distributed Exhaust

The category of Distributed Exhaust entails using a central engine powerplant with a ducted nozzle(s) for strategic deployment of thrust on the aircraft. Distributed exhaust configurations suffer nozzle viscous losses in performance and will likely only "buy their way on" to aircraft systems exhibiting extreme sensitivity to low-speed li ft and/or cru ise drag. Therefore, distributed exhaust systems will be better suited to supersonic cruise applications, where noise-sizing for takeoff fie ld length and sustained supersonic cruise drag are the most dominant and least reconcilable constraints (Figure 7).

High aspect ratio nozzles for commercial supersonic cru ise vehicles promise both noise and nozzle weight reduction potential. The projected sideline noise reduction using a wing trailing edge 2-D mixer/ejector nozzle with comparatively small exhaust height may be as much as I OdB (due to increased ambient jet mixing, improved ejector internal penetration and mixing, and increased liner attenuabi li ty resulting from naturally higher frequencies and surface areas). In addition, the high aspect ratio geometrically produces a shorter nozzle for an equal nozzle

engine manufacturing tolerances and corresponding impacts on seals and clearances, 3-D turbomachinery shapes, and combustion efficiency are primary technical challenges for these propulsion systems. Currently, parts at the micro-scale can only be produced in two dimensions, resembling extruded parts. This efficiency limitation on the rotating components will be overcome with material and manufacturing technologies. These will enable three­dimensional shaping of airfoils and allowing new micro­scale engine configurations with reduced stress concentrations inherent in the current two-dimensional prototypes. Other factors affecting the structural/mechanical design of these micro-engines are the typically high rotational speeds, which may exceed 2 million RPMs. These high speeds are achievable due to reduced-scale inertial loads, but will demand non­lubricated air-bearings to surpass the common modes of failure observed in research prototypes.

Though the physical engine scale is decreased, the chemical reaction times remain constant and will require technology innovation to regain lost combustion efficiency. A very general rule for mini- and micro-engines is that both specific fuel consumption (SFC) and thrust-to-weight ratio increase as thrust and size decrease. To become a viable primary propulsion source, SFC reductions to near current macro-engine levels must accompany the increased thrust­to-weight ratios already achievab le in mini and micro engines.

Distributed engine concepts will enab le a var iety of attractive airframe configurations affording both performance and operational benefits. Large engine production rates, lower development cost and cycle time, and line-replaceable-unit elimination of on-the-wing engine maintenance could reduce the life cycle cost by as much as 50%. Aircraft safety will be enhanced through engine redundancy and semi-redundant propulsion control of the aircraft. Dual use of the ai rframe structure will dramatically reduce the overall system weight, and afford holistic system noise reduction opportunities beyond those attainable with discrete engines. Principle technologies that will afford the greatest potential for realizing micro engine propu lsion success include: innovative combustion techniques, processing of SiC and other advanced micro engine material for improved 3D designs, and integral autonomous controls coupled with sub-micro sensors assuring engine array reliability.

Common-Core Multi- FanslPropulsors

The category of Common-Core Multi-FanslPropulsors entails the packaging of multiple thrust fans powered by a central engi ne core (Figure 6). The advantage of these configurations is that they provide ultra high BPR engine with higher propulsive efficiency without necessitating radical ai rframe changes (such as high wing designs) to accommodate a single large turbofan engine. The principle challenges of this approach are power transmission weight and losses. These challenges may be somewhat mitigated by the variable gearbox technologies previously developed under the Gas Turbine Revolution, or by emp loying blade-on-blade manifolded tip-turbines on the fans. These challenges could also be circumvented

5

IGTC03-ABS-066b

using direct-drive tandem fans (i.e. axially aligned fans with separate inlets for and aft of the common core) rather than the s ide-by-side configuration. Another potential configuration uses the core exhaust to drive two off-axis turbines that are attached to direct-drive fans. Multi-fan cores will require innovative separate inlets to realize their full BPR and aircraft integration benefit. This will require lightweight structures and possibly flow control to minimize weight and inlet performance losses.

The commonly shared performance challenges assoc iated with all forms of distributed propulsion (Iow­Reynolds number flows, boundary-l ayer interactions, and fuel management systems) will be surpassed during this research phase using those technologies and discipline capabilities (aerodynamic, mechanical, materials, structures, manufacturing, etc.) outlined for the Gas Turbine Revolution . The highly integrated Distributed Vectored Propulsion systems for future subsonic and superson ic transports will incorporate V/STOL and Propulsion Controlled Aircraft (PCA) capabilities, and capitalize on intelligent, self-healing properties.

Fig. 6 Common-Core, Multi-Propulsor Engines

Distributed Exhaust

The category of Distributed Exhaust entails using a central engine powerplant with a ducted nozzle(s) for strategic deployment of thrust on the aircraft. Distributed exhaust configurations suffer nozzle viscous losses in performance and will likely only "buy their way on" to aircraft systems exhibiting extreme sensitivity to low-speed li ft and/or cru ise drag. Therefore, distributed exhaust systems will be better suited to supersonic cruise applications, where noise-sizing for takeoff fie ld length and sustained supersonic cruise drag are the most dominant and least reconcilable constraints (Figure 7).

High aspect ratio nozzles for commercial supersonic cru ise vehicles promise both noise and nozzle weight reduction potential. The projected sideline noise reduction using a wing trailing edge 2-D mixer/ejector nozzle with comparatively small exhaust height may be as much as I OdB (due to increased ambient jet mixing, improved ejector internal penetration and mixing, and increased liner attenuabi li ty resulting from naturally higher frequencies and surface areas). In addition, the high aspect ratio geometrically produces a shorter nozzle for an equal nozzle

pressure ratio and provides the potential for shared structural loading with the wing. This will culminate in as much as 50% equivalent nozzle weight reduction and propulsion related cruise drag. Increased low-speed lift via wi ng trailing edge flap blowing and thrust vectoring will also be achieved through this configuration, and reduce the required takeoff fie ld length and affording community and approach noise reductions. Hybrid systems incorporating distributed/thrust vectored exhaust and micro-engine for flow control and actuator power are also attractive. To reduce the performance loss of the increased nozzle surface areas and increased internal flow turning, micro-engi nes can be incorporated for boundary layer control and cooling. This approach might passively utilize waste heat from the nozzle to power the micro-engines rather than active dedicated micro­fuel /combustors. The scavenging of waste heat will reduce the exhaust temperatures as well as increase the effectiveness of the primary distributed propulsion system. The micro engines might also be configured to facilitate virtual shape control through fluidic "reshaping" of the primary nozzles. This reduces or eliminates mechanical actuation wh ile reducing internal viscous losses and waste heat.

Fig. 7 Supersonic Airplane with High Aspect Ratio Nozzle

ALTERNATE ENERGY PROPULSION

While the tim ing remains debatable, the 21 51 Century will almost assured ly see the emergence of an all -electric economy. In this era, electricity will be the common currency. It will be produced, stored, converted and consumed as other exchange medium are today. Preced ing this inevitab le end is the likelihood of the hydrogen-fuel economy. The ever-increas ing global energy consumption rate for electric ground power and the transportation industries w ill continue to drain global reserves of crude oil Global environmental impacts from hydrocarbon emissions will accelerate the introduction of cleaner alternative energy sources and more effic ient utilization systems for both the ground power and transportation industries.

The transportation industry energy alternative will include low-carbon fue ls and additives, hydrogen fuel , stored electrochemical, and electromechanical energy sources . Future 21 51 Century aeropropulsion systems and aviation systems must align to best utilize these future available energy sources. The cost associated with

6

IGTC03-ABS-066b

infrastructure changes and the sustai ned use of legacy aviation systems log ically demands a transition period as new energy sources are introduced. Hybrid propulsion systems will be required in order to meet the challenges of transition and time ly introduction of fled gling new power systems.

A global hydrogen consumption rate for future power demands a practical, cost effective production rate. This implies hydrogen production from water, using a net­positive (and as yet undetermined) energy means. Safety issues (whether real or perceived) will also govern the production, distribution, and storage of hydrogen. Complexities associated wi th hydrogen production and densification compounded by safety issues will likely result in centralized " refineries". These will be similar to present­day hydrocarbon fuel refineries, despite the global ava ilability of water. Airports will also require on-site handling of hydrogen. Early acceptance of hydrogen at controlled-access airport facilities will also promote the introduction of hybrid combustion/electric propulsion such as the gas-turbine/fuel-cell.

Recent advances in fuel cell technology and electrical component power densities, promoted by automotive and other transportation sectors, wi ll eventually displace combustion-based propulsion in the aviation industry. In summary, the 21 51 Century will see an environmental­inspired revo lution in the transportation system from hydrocarbon combustion power to electric power. Possibly hydrogen fuel and hybrid combustion/electric systems may bridge the transitions.

Fuel Cell Powered Aircrafts

Fuel cells are becoming a viable option for small aircraft propulsion and Auxiliary Power Units (APUs) and hold future promise for large-scale commercial aircraft (Figure 8). Doubling of fuel cell power densities can be achieved in the next five years. This would make electrically powered light general aviation aircraft possible with no performance penalties compared to their conventionally powered counterparts. Preliminary results from a recent NASA study (Berton, et. al. 2003) indicate that flight is possible using off-the-shelf fuel cell and power management technology levels, albeit at reduced speed, climb rate, range, and payload-carrying capability. Aircraft performance appears sufficient to fly a technology demonstration, proof-of-concept type vehicle using today's automotive-derived fuel cell and power systems. Only light aircraft are anticipated to be feasible with near-term technology due to their relatively low, automobile-like power requirements.

The increase in power density would also make fuel cell APUs for larger aircraft viable. NASA is working with Boeing to explore a possibility of development and demonstration of a Solid Oxide Fuel Cell (SOFC) APU for a large transport by building on DOE's successes in SOFC. The current gas turbine APUs operate at about 14% load cycle efficiency contributing 20% of the airport ground based emissions. A fuel cell APU will lead to near zero emissions, lower noise, and could reduce aircraft fuel consumption. A full time, integrated power unit will

pressure ratio and provides the potential for shared structural loading with the wing. This will culminate in as much as 50% equivalent nozzle weight reduction and propulsion related cruise drag. Increased low-speed lift via wi ng trailing edge flap blowing and thrust vectoring will also be achieved through this configuration, and reduce the required takeoff fie ld length and affording community and approach noise reductions. Hybrid systems incorporating distributed/thrust vectored exhaust and micro-engine for flow control and actuator power are also attractive. To reduce the performance loss of the increased nozzle surface areas and increased internal flow turning, micro-engi nes can be incorporated for boundary layer control and cooling. This approach might passively utilize waste heat from the nozzle to power the micro-engines rather than active dedicated micro­fuel /combustors. The scavenging of waste heat will reduce the exhaust temperatures as well as increase the effectiveness of the primary distributed propulsion system. The micro engines might also be configured to facilitate virtual shape control through fluidic "reshaping" of the primary nozzles. This reduces or eliminates mechanical actuation wh ile reducing internal viscous losses and waste heat.

Fig. 7 Supersonic Airplane with High Aspect Ratio Nozzle

ALTERNATE ENERGY PROPULSION

While the tim ing remains debatable, the 21 51 Century will almost assured ly see the emergence of an all -electric economy. In this era, electricity will be the common currency. It will be produced, stored, converted and consumed as other exchange medium are today. Preced ing this inevitab le end is the likelihood of the hydrogen-fuel economy. The ever-increas ing global energy consumption rate for electric ground power and the transportation industries w ill continue to drain global reserves of crude oil Global environmental impacts from hydrocarbon emissions will accelerate the introduction of cleaner alternative energy sources and more effic ient utilization systems for both the ground power and transportation industries.

The transportation industry energy alternative will include low-carbon fue ls and additives, hydrogen fuel , stored electrochemical, and electromechanical energy sources . Future 21 51 Century aeropropulsion systems and aviation systems must align to best utilize these future available energy sources. The cost associated with

6

IGTC03-ABS-066b

infrastructure changes and the sustai ned use of legacy aviation systems log ically demands a transition period as new energy sources are introduced. Hybrid propulsion systems will be required in order to meet the challenges of transition and time ly introduction of fled gling new power systems.

A global hydrogen consumption rate for future power demands a practical, cost effective production rate. This implies hydrogen production from water, using a net­positive (and as yet undetermined) energy means. Safety issues (whether real or perceived) will also govern the production, distribution, and storage of hydrogen. Complexities associated wi th hydrogen production and densification compounded by safety issues will likely result in centralized " refineries". These will be similar to present­day hydrocarbon fuel refineries, despite the global ava ilability of water. Airports will also require on-site handling of hydrogen. Early acceptance of hydrogen at controlled-access airport facilities will also promote the introduction of hybrid combustion/electric propulsion such as the gas-turbine/fuel-cell.

Recent advances in fuel cell technology and electrical component power densities, promoted by automotive and other transportation sectors, wi ll eventually displace combustion-based propulsion in the aviation industry. In summary, the 21 51 Century will see an environmental­inspired revo lution in the transportation system from hydrocarbon combustion power to electric power. Possibly hydrogen fuel and hybrid combustion/electric systems may bridge the transitions.

Fuel Cell Powered Aircrafts

Fuel cells are becoming a viable option for small aircraft propulsion and Auxiliary Power Units (APUs) and hold future promise for large-scale commercial aircraft (Figure 8). Doubling of fuel cell power densities can be achieved in the next five years. This would make electrically powered light general aviation aircraft possible with no performance penalties compared to their conventionally powered counterparts. Preliminary results from a recent NASA study (Berton, et. al. 2003) indicate that flight is possible using off-the-shelf fuel cell and power management technology levels, albeit at reduced speed, climb rate, range, and payload-carrying capability. Aircraft performance appears sufficient to fly a technology demonstration, proof-of-concept type vehicle using today's automotive-derived fuel cell and power systems. Only light aircraft are anticipated to be feasible with near-term technology due to their relatively low, automobile-like power requirements.

The increase in power density would also make fuel cell APUs for larger aircraft viable. NASA is working with Boeing to explore a possibility of development and demonstration of a Solid Oxide Fuel Cell (SOFC) APU for a large transport by building on DOE's successes in SOFC. The current gas turbine APUs operate at about 14% load cycle efficiency contributing 20% of the airport ground based emissions. A fuel cell APU will lead to near zero emissions, lower noise, and could reduce aircraft fuel consumption. A full time, integrated power unit will

pressure ratio and provides the potential for shared structural loading with the wing. This will culminate in as much as 50% equivalent nozzle weight reduction and propulsion related cruise drag. Increased low-speed lift via wi ng trailing edge flap blowing and thrust vectoring will also be achieved through this configuration, and reduce the required takeoff fie ld length and affording community and approach noise reductions. Hybrid systems incorporating distributed/thrust vectored exhaust and micro-engine for flow control and actuator power are also attractive. To reduce the performance loss of the increased nozzle surface areas and increased internal flow turning, micro-engi nes can be incorporated for boundary layer control and cooling. This approach might passively utilize waste heat from the nozzle to power the micro-engines rather than active dedicated micro­fuel /combustors. The scavenging of waste heat will reduce the exhaust temperatures as well as increase the effectiveness of the primary distributed propulsion system. The micro engines might also be configured to facilitate virtual shape control through fluidic "reshaping" of the primary nozzles. This reduces or eliminates mechanical actuation wh ile reducing internal viscous losses and waste heat.

Fig. 7 Supersonic Airplane with High Aspect Ratio Nozzle

ALTERNATE ENERGY PROPULSION

While the tim ing remains debatable, the 21 51 Century will almost assured ly see the emergence of an all -electric economy. In this era, electricity will be the common currency. It will be produced, stored, converted and consumed as other exchange medium are today. Preced ing this inevitab le end is the likelihood of the hydrogen-fuel economy. The ever-increas ing global energy consumption rate for electric ground power and the transportation industries w ill continue to drain global reserves of crude oil Global environmental impacts from hydrocarbon emissions will accelerate the introduction of cleaner alternative energy sources and more effic ient utilization systems for both the ground power and transportation industries.

The transportation industry energy alternative will include low-carbon fue ls and additives, hydrogen fuel , stored electrochemical, and electromechanical energy sources . Future 21 51 Century aeropropulsion systems and aviation systems must align to best utilize these future available energy sources. The cost associated with

6

IGTC03-ABS-066b

infrastructure changes and the sustai ned use of legacy aviation systems log ically demands a transition period as new energy sources are introduced. Hybrid propulsion systems will be required in order to meet the challenges of transition and time ly introduction of fled gling new power systems.

A global hydrogen consumption rate for future power demands a practical, cost effective production rate. This implies hydrogen production from water, using a net­positive (and as yet undetermined) energy means. Safety issues (whether real or perceived) will also govern the production, distribution, and storage of hydrogen. Complexities associated wi th hydrogen production and densification compounded by safety issues will likely result in centralized " refineries". These will be similar to present­day hydrocarbon fuel refineries, despite the global ava ilability of water. Airports will also require on-site handling of hydrogen. Early acceptance of hydrogen at controlled-access airport facilities will also promote the introduction of hybrid combustion/electric propulsion such as the gas-turbine/fuel-cell.

Recent advances in fuel cell technology and electrical component power densities, promoted by automotive and other transportation sectors, wi ll eventually displace combustion-based propulsion in the aviation industry. In summary, the 21 51 Century will see an environmental­inspired revo lution in the transportation system from hydrocarbon combustion power to electric power. Possibly hydrogen fuel and hybrid combustion/electric systems may bridge the transitions.

Fuel Cell Powered Aircrafts

Fuel cells are becoming a viable option for small aircraft propulsion and Auxiliary Power Units (APUs) and hold future promise for large-scale commercial aircraft (Figure 8). Doubling of fuel cell power densities can be achieved in the next five years. This would make electrically powered light general aviation aircraft possible with no performance penalties compared to their conventionally powered counterparts. Preliminary results from a recent NASA study (Berton, et. al. 2003) indicate that flight is possible using off-the-shelf fuel cell and power management technology levels, albeit at reduced speed, climb rate, range, and payload-carrying capability. Aircraft performance appears sufficient to fly a technology demonstration, proof-of-concept type vehicle using today's automotive-derived fuel cell and power systems. Only light aircraft are anticipated to be feasible with near-term technology due to their relatively low, automobile-like power requirements.

The increase in power density would also make fuel cell APUs for larger aircraft viable. NASA is working with Boeing to explore a possibility of development and demonstration of a Solid Oxide Fuel Cell (SOFC) APU for a large transport by building on DOE's successes in SOFC. The current gas turbine APUs operate at about 14% load cycle efficiency contributing 20% of the airport ground based emissions. A fuel cell APU will lead to near zero emissions, lower noise, and could reduce aircraft fuel consumption. A full time, integrated power unit will

improve operational effectiveness by replacing multiple secondary power systems with a si ngle "so ld-state" device. A five-fold increase in fuel cell power density would enable electrically powered regional/commuter size aircraft. A ten-fold increase would enable electrically powered large commercial passenger aircraft. Advanced fuel cell and power management technologies will be needed to achieve comparable aircraft performance and utility and to enable the design of larger electric aircraft.

12 r-----------------------~~~. ~~,~CO~"'"~,,~~;~"' ~P.~~"~~.

1960

Io.ro!.i hM.:rGL-"': III 7·rold Incr..:tl~ an AJ~.lllllc ,,"h.T ))1..""11\ III 1\1II(1OIOtl\''': r(l\h.'" ~1S1h

1970

l(ty..:::~ I11;YO:;If!C

1980 1990

Calendar

2000

Alrtmn (lO\' SOAlnl'n.-:lw)

2010 2020

Fig. 8 Potential Fuel Cell Evolution Towards Meeting Future Aircraft Transportation Needs

The benefits offuel cell powered aircraft are very low to zero emissions, simpler more reliable power and propulsion systems providing increased safety and lower maintenance costs; and greatly reduced noise from the power generator portion of the propulsion systems. Some of the critical challenges are fuel cell and power management system weight and hydrogen fuel system volume. Heat management is critical to the practical operation of any fuel cell-powered app lication and requires more rigorous modeling. An efficient, safe airport hydrogen fueling infrastructure also must be in place if electric aircraft are to be economically viable. A global hydrogen economy also remains elusive.

Capitalizing on the micro-manufacturing technologies characterized for Distributed Vectored Propulsion, micro­fuel cells and other electrochemical and pure electric storage devices (such as super batteries and capacitors) will be made small enough and in sufficient quantity as to allow viable all-electric propulsion. These devices will be integrated within the ai rcraft, taking full advantage of structural load sharing and dual-functioning systems (e.g. distributed propulsion and controls). These and other electrical components (such as high-temperature superconductors) will benefit from the ever-improving electronics industry in terms of their capabi lity and affordability.

The electrically-powered subsonic transports of the future wi ll likely be powered by small, distributed motors and fans (Figure 9). Similar in configuration to the wing­span distributed engines, these configurations will utilize

7

IGTC03-ABS-066b

remote fans and motors to achieve forward propulsion, and may be coupled with blown wing/flaps for high lift at takeoff. The primary advantage of these configurations is the use of a centralized, highly efficient core power unit. This may be in the form of fuel cells or centralized gas turbine APUs. Electric power transmission to the remote fans is a safer more efficient approach than independent distributed fuel delivery systems (as would be utilized by the distributed engines). In the case of the APU configuration, the excess APU power could also be used in flight to meet the increasing passenger/aircraft demand for electric power and communications. In the case of multiple side-by-side fans sharing a common 2D wing integrated inlet, the benefits of boundary layer ingestion (previously discussed) may also be realized . The primary challenges for this type of propulsion will be the motor weight (many small motors with independent structures (inefficient power conversion density) versus fewer, larger heavy motors).

Fig. 9 Fuel Cell Wing with Distributed Propulsors

Variable speed motors, leveraging the adaptive engine and controls from the Gas Turbine Revolution and the distributed fans from the Engine Configuration Revolution, will be produced from lightweight superconducting technologies born of the Alternate Energy & Power Revolution. The culmination of these and other contributing techno logies in a single adaptive system will power a variety of future transport aircraft, while assuring safe environmental 24-hour operation.

SUMMARY

Propu lsion system advances have been the fundamental drivers toward the progress made in air transportation and will continue into the 21 st Century. Enormous advances in propulsion performance, emissions and efficiency have made it possib le for aircraft to travel at higher speeds safely over longer ranges. Over the last ten years NASA, working with other federal agencies and industry partners, have developed aeropropulsion technologies that when fully implemented will reduce aircraft emissions by 70%, engine noise levels by 6 dB and improved fuel consumption by 15%. To continue this trend and each the ultimate goal of an emission less, silent aircraft, NASA has identified a series of propulsion system technology revolutions that will be essential to meet the

improve operational effectiveness by replacing multiple secondary power systems with a si ngle "so ld-state" device. A five-fold increase in fuel cell power density would enable electrically powered regional/commuter size aircraft. A ten-fold increase would enable electrically powered large commercial passenger aircraft. Advanced fuel cell and power management technologies will be needed to achieve comparable aircraft performance and utility and to enable the design of larger electric aircraft.

12 r-----------------------~~~. ~~,~CO~"'"~,,~~;~"' ~P.~~"~~.

1960

Io.ro!.i hM.:rGL-"': III 7·rold Incr..:tl~ an AJ~.lllllc ,,"h.T ))1..""11\ III 1\1II(1OIOtl\''': r(l\h.'" ~1S1h

1970

l(ty..:::~ I11;YO:;If!C

1980 1990

Calendar

2000

Alrtmn (lO\' SOAlnl'n.-:lw)

2010 2020

Fig. 8 Potential Fuel Cell Evolution Towards Meeting Future Aircraft Transportation Needs

The benefits offuel cell powered aircraft are very low to zero emissions, simpler more reliable power and propulsion systems providing increased safety and lower maintenance costs; and greatly reduced noise from the power generator portion of the propulsion systems. Some of the critical challenges are fuel cell and power management system weight and hydrogen fuel system volume. Heat management is critical to the practical operation of any fuel cell-powered app lication and requires more rigorous modeling. An efficient, safe airport hydrogen fueling infrastructure also must be in place if electric aircraft are to be economically viable. A global hydrogen economy also remains elusive.

Capitalizing on the micro-manufacturing technologies characterized for Distributed Vectored Propulsion, micro­fuel cells and other electrochemical and pure electric storage devices (such as super batteries and capacitors) will be made small enough and in sufficient quantity as to allow viable all-electric propulsion. These devices will be integrated within the ai rcraft, taking full advantage of structural load sharing and dual-functioning systems (e.g. distributed propulsion and controls). These and other electrical components (such as high-temperature superconductors) will benefit from the ever-improving electronics industry in terms of their capabi lity and affordability.

The electrically-powered subsonic transports of the future wi ll likely be powered by small, distributed motors and fans (Figure 9). Similar in configuration to the wing­span distributed engines, these configurations will utilize

7

IGTC03-ABS-066b

remote fans and motors to achieve forward propulsion, and may be coupled with blown wing/flaps for high lift at takeoff. The primary advantage of these configurations is the use of a centralized, highly efficient core power unit. This may be in the form of fuel cells or centralized gas turbine APUs. Electric power transmission to the remote fans is a safer more efficient approach than independent distributed fuel delivery systems (as would be utilized by the distributed engines). In the case of the APU configuration, the excess APU power could also be used in flight to meet the increasing passenger/aircraft demand for electric power and communications. In the case of multiple side-by-side fans sharing a common 2D wing integrated inlet, the benefits of boundary layer ingestion (previously discussed) may also be realized . The primary challenges for this type of propulsion will be the motor weight (many small motors with independent structures (inefficient power conversion density) versus fewer, larger heavy motors).

Fig. 9 Fuel Cell Wing with Distributed Propulsors

Variable speed motors, leveraging the adaptive engine and controls from the Gas Turbine Revolution and the distributed fans from the Engine Configuration Revolution, will be produced from lightweight superconducting technologies born of the Alternate Energy & Power Revolution. The culmination of these and other contributing techno logies in a single adaptive system will power a variety of future transport aircraft, while assuring safe environmental 24-hour operation.

SUMMARY

Propu lsion system advances have been the fundamental drivers toward the progress made in air transportation and will continue into the 21 st Century. Enormous advances in propulsion performance, emissions and efficiency have made it possib le for aircraft to travel at higher speeds safely over longer ranges. Over the last ten years NASA, working with other federal agencies and industry partners, have developed aeropropulsion technologies that when fully implemented will reduce aircraft emissions by 70%, engine noise levels by 6 dB and improved fuel consumption by 15%. To continue this trend and each the ultimate goal of an emission less, silent aircraft, NASA has identified a series of propulsion system technology revolutions that will be essential to meet the

improve operational effectiveness by replacing multiple secondary power systems with a si ngle "so ld-state" device. A five-fold increase in fuel cell power density would enable electrically powered regional/commuter size aircraft. A ten-fold increase would enable electrically powered large commercial passenger aircraft. Advanced fuel cell and power management technologies will be needed to achieve comparable aircraft performance and utility and to enable the design of larger electric aircraft.

12 r-----------------------~~~. ~~,~CO~"'"~,,~~;~"' ~P.~~"~~.

1960

Io.ro!.i hM.:rGL-"': III 7·rold Incr..:tl~ an AJ~.lllllc ,,"h.T ))1..""11\ III 1\1II(1OIOtl\''': r(l\h.'" ~1S1h

1970

l(ty..:::~ I11;YO:;If!C

1980 1990

Calendar

2000

Alrtmn (lO\' SOAlnl'n.-:lw)

2010 2020

Fig. 8 Potential Fuel Cell Evolution Towards Meeting Future Aircraft Transportation Needs

The benefits offuel cell powered aircraft are very low to zero emissions, simpler more reliable power and propulsion systems providing increased safety and lower maintenance costs; and greatly reduced noise from the power generator portion of the propulsion systems. Some of the critical challenges are fuel cell and power management system weight and hydrogen fuel system volume. Heat management is critical to the practical operation of any fuel cell-powered app lication and requires more rigorous modeling. An efficient, safe airport hydrogen fueling infrastructure also must be in place if electric aircraft are to be economically viable. A global hydrogen economy also remains elusive.

Capitalizing on the micro-manufacturing technologies characterized for Distributed Vectored Propulsion, micro­fuel cells and other electrochemical and pure electric storage devices (such as super batteries and capacitors) will be made small enough and in sufficient quantity as to allow viable all-electric propulsion. These devices will be integrated within the ai rcraft, taking full advantage of structural load sharing and dual-functioning systems (e.g. distributed propulsion and controls). These and other electrical components (such as high-temperature superconductors) will benefit from the ever-improving electronics industry in terms of their capabi lity and affordability.

The electrically-powered subsonic transports of the future wi ll likely be powered by small, distributed motors and fans (Figure 9). Similar in configuration to the wing­span distributed engines, these configurations will utilize

7

IGTC03-ABS-066b

remote fans and motors to achieve forward propulsion, and may be coupled with blown wing/flaps for high lift at takeoff. The primary advantage of these configurations is the use of a centralized, highly efficient core power unit. This may be in the form of fuel cells or centralized gas turbine APUs. Electric power transmission to the remote fans is a safer more efficient approach than independent distributed fuel delivery systems (as would be utilized by the distributed engines). In the case of the APU configuration, the excess APU power could also be used in flight to meet the increasing passenger/aircraft demand for electric power and communications. In the case of multiple side-by-side fans sharing a common 2D wing integrated inlet, the benefits of boundary layer ingestion (previously discussed) may also be realized . The primary challenges for this type of propulsion will be the motor weight (many small motors with independent structures (inefficient power conversion density) versus fewer, larger heavy motors).

Fig. 9 Fuel Cell Wing with Distributed Propulsors

Variable speed motors, leveraging the adaptive engine and controls from the Gas Turbine Revolution and the distributed fans from the Engine Configuration Revolution, will be produced from lightweight superconducting technologies born of the Alternate Energy & Power Revolution. The culmination of these and other contributing techno logies in a single adaptive system will power a variety of future transport aircraft, while assuring safe environmental 24-hour operation.

SUMMARY

Propu lsion system advances have been the fundamental drivers toward the progress made in air transportation and will continue into the 21 st Century. Enormous advances in propulsion performance, emissions and efficiency have made it possib le for aircraft to travel at higher speeds safely over longer ranges. Over the last ten years NASA, working with other federal agencies and industry partners, have developed aeropropulsion technologies that when fully implemented will reduce aircraft emissions by 70%, engine noise levels by 6 dB and improved fuel consumption by 15%. To continue this trend and each the ultimate goal of an emission less, silent aircraft, NASA has identified a series of propulsion system technology revolutions that will be essential to meet the

challenge of 21 Sl Century commercial ai r transportation. Future propulsion systems have been presented including intelligent engines, distributed vectored propulsion systems based on mini/micro engines, and fuel cell powered mini­fans . These advanced propulsion systems hold the potenti al to enable conti.nued improvements in perfo rmance and emissions requ ired to achieve the vision of an affordable, emissionless, and silent ai rcraft.

References

Lytle, J. K., Follen, G. J., Nai man, C. G. , Evans, A. L. , Veres, 1. P., and ET. AL., 1999 Numerical Propulsion System Simulation Industry Review, NASNTR 209795, September 6, 2000.

Berton, 1. 1., Freeh, J. E., and Wickenhe iser, T. J., "An Analytical Performance Assessment of a Fuel Cell­Powered, Small Electric Airplane," Symposium on Novel and Emerging Vehicle Technology Concepts, Brussels, Belgium, April 7-11 , 2003.

IGTC03-ABS-066b

8

challenge of 21 Sl Century commercial ai r transportation. Future propulsion systems have been presented including intelligent engines, distributed vectored propulsion systems based on mini/micro engines, and fuel cell powered mini­fans . These advanced propulsion systems hold the potenti al to enable conti.nued improvements in perfo rmance and emissions requ ired to achieve the vision of an affordable, emissionless, and silent ai rcraft.

References

Lytle, J. K., Follen, G. J., Nai man, C. G. , Evans, A. L. , Veres, 1. P., and ET. AL., 1999 Numerical Propulsion System Simulation Industry Review, NASNTR 209795, September 6, 2000.

Berton, 1. 1., Freeh, J. E., and Wickenhe iser, T. J., "An Analytical Performance Assessment of a Fuel Cell­Powered, Small Electric Airplane," Symposium on Novel and Emerging Vehicle Technology Concepts, Brussels, Belgium, April 7-11 , 2003.

IGTC03-ABS-066b

8

challenge of 21 Sl Century commercial ai r transportation. Future propulsion systems have been presented including intelligent engines, distributed vectored propulsion systems based on mini/micro engines, and fuel cell powered mini­fans . These advanced propulsion systems hold the potenti al to enable conti.nued improvements in perfo rmance and emissions requ ired to achieve the vision of an affordable, emissionless, and silent ai rcraft.

References

Lytle, J. K., Follen, G. J., Nai man, C. G. , Evans, A. L. , Veres, 1. P., and ET. AL., 1999 Numerical Propulsion System Simulation Industry Review, NASNTR 209795, September 6, 2000.

Berton, 1. 1., Freeh, J. E., and Wickenhe iser, T. J., "An Analytical Performance Assessment of a Fuel Cell­Powered, Small Electric Airplane," Symposium on Novel and Emerging Vehicle Technology Concepts, Brussels, Belgium, April 7-11 , 2003.

IGTC03-ABS-066b

8